Air Fronts: Airdromes - FM-26, Defense of Airdromes - Chapter 6. Passive Defense
SECTION I: DISPERSION
63. GENERAL.-Dispersion is an essential measure in the passive defense of an airdrome. Normally there should be nothing in the landing area but those planes which are on the alert.
64. AIRCRAFT.-It is of the utmost importance to avoid the grouping of aircraft on the ground. Planes not in revetments should be in groups of three planes, each plane at least 150 yards from the next and each group at least 200 yards from any plane or other group. Revetments should be 150 feet apart in similar groups. Airplanes, revetted or unrevetted, must not be parked along straight lines nor in continuation of the runways or other natural bombing or strafing runs. Fighter aircraft are kept near the down-wind ends of the runways, ready to take off with a minimum loss of time in the event of an attack. Special precautions should be taken at night to disperse planes which are not on the night alert. If planes are not to be flown, they are moved off the field. Bombardment and reconnaissance planes are dispersed at some distance from the airdrome. A mile is not excessive if it facilitates concealment. Extent of dispersal depends, however, not only on local terrain but also on the requirements for protecting the aircraft from sabotage or from possible airborne action. Parked planes at airdromes within range of enemy fighters must not be dispersed so widely that they are not under the cover of antiaircraft fire.
65. INSTALLATIONS AND HOUSING.-Technical and operational installations are located near the landing area, but a formalized arrangement should be avoided. Only the control tower need be in the immediate vicinity of the runways. Base operations should be off the edge of the field and away from conspicuous features of the runways or prominent land-marks. It should have no standard location with respect to other airdrome features or similar installations at other airdromes. The engineering maintenance area should be as far removed from the landing area as conditions permit. Thorough reconnaissance of the area should be undertaken to find suitable areas for the housing of personnel. The fullest possible use should be made of existing structures, and new ones should be designed and sited to conform to those normally found in the region.
66. STORAGE.-Fixed servicing and supply facilities are not built at field airdromes. Gasoline, ammunition, bombs, and other supplies are delivered to aircraft at dispersed locations from dispersed stores. Armament and fuel supply points should be well away from the airdrome and isolated from all other equipment, materiel, or dispersal areas. Stores of gasoline in drums should be at least 150 feet apart, if given a protective earth traverse on all sides. Without such protection storage piles should be spaced at 200 yards. Ammunition, bombs, pyrotechnic, and chemical stores should be dispersed under the direction of ordnance personnel or in accordance with the standard safety distances given the Ordnance Safety Manual.
67. REFERENCE.-See TM 5-255 for specific distances and details of dispersion.
SECTION II: Cover
68. PERSONNEL.-At all installations such as headquarters, supply points, engineering maintenance, aircraft dispersal areas, and defense positions, and in all housing areas or any place habitually occupied, air raid shelters must be provided for personnel. The special trench, braced to resist earth shock, is the simplest protection and one of the best. The trace of these trenches is either a chevron or an L to permit occupants to take shelter in a leg which is perpendicular to the direction of flight of a strafing plane. If it is not possible to dig trenches because of the soil, effective protection against heavy machine-gun fire can be had by setting up oil drums filled with sand. For aircraft combat crews, overhead cover, sufficient at least to withstand splinters, must be provided if they are to secure the rest to perform their subsequent missions without undue loss of men and material. Dugouts can be made to serve.
69. AIRCRAFT.-Revetments provide supplementary protection for dispersed aircraft. They reduce damage from bomb fragments but do not prevent effective strafing. They draw fire if they are not well concealed, and they are extremely hard to camouflage. The commander of the airdrome should determine whether or not they are to be constructed. A War Department order prohibits their construction in the continental United States without specific authority. Elaborate revetments are seldom constructed. Good ones can be constructed quickly by throwing up U-shaped embankments of earth high enough to hide a plane from horizontal view. Their openings should face in different directions. Sand bags filled with the spoil from other works can be used for their construction. Sunken revetments are inadvisable.
70. STORES AND EQUIPMENT.-Normally, all storage at field airdromes will be above ground in dispersed revetments. For bombs and other supplies which are not affected by the weather, open storage in revetted traverses is ample. The quantity of supplies on hand at advanced field airdromes does not normally justify attempting to give them protection against small-arms fire or bombs. If warehouses are built, they should be theater of operations type. All storage facilities should be carefully camouflaged. Machine tools should be protected by surrounding walls of concrete or sandbags. If they are in trailers, the parked vehicles should be revetted with earth or sandbags at semipermanent establishments. Under special conditions it may be necessary to construct theater of operations type of buildings to house the power tools.
FIGURE 17.-Bomb storage in revetment.
71. REFERENCE.-See TM 5-255 for details of method and construction of cover.
SECTION III: CAMOUFLAGE
72. GENERAL.-Camouflage is any and every means of concealing, disguising, or obscuring the airdrome or its installations, planes, materiel, and personnel so that the enemy finds it difficult to recognize or identify his target. The extreme importance of taking adequate camouflage measures cannot be overstressed. Continuous and effective efforts for disguise or concealment are vital to the defense of an airdrome. Camouflage discipline must be thorough and rigorously observed. Troops and installations unsatisfactorily camouflaged are not likely to survive for local defense or for any other mission. The more successful the deception, the less the airdrome will look like an airdrome, the less attention it will draw from the enemy. The more effective the camouflage, the more installations and the more personnel will endure for attack and defense. Although camouflage officers of the aviation engineers are available for technical advice and the planning of large-scale projects, camouflage is the job of all personnel, who must be indoctrinated with the necessity of constant effort and vigilance and made to understand the underlying principles of good camouflage as well as the means and methods of achieving it. What hundreds have labored to do, one can carelessly or thoughtlessly undo. Good camouflage in the field does not of necessity demand elaborate prefabricated materials nor specially schooled direction and labor. Time spent in careful planning and common sense employed in the use of existing local cover and concealment and local materials, supplemented if necessary with simple artificial devices, will result in good camouflage, while no amount of special equipment will take the place of thoughtful planning and good camouflage discipline. If it is realized what will give a position away to the enemy, much equipment and labor will not be needed to disguise it. If it is not realized what will give a position away, all the equipment in a base supply depot will not suffice.
73. REFERENCES.-Detailed information and instructions relating to camouflage can be found in FM 5-20 and in TM 5-255, 5-266, and 5-267 and its supplements.
SECTION IV: OBSTACLES
74. GENERAL.-Obstacles of all types have become increasingly important. They are used at airdromes for three general purposes: to prevent the safe landing of enemy air-craft; to impede the advance of mechanized vehicles; and to hinder the attack of foot elements. Temporary obstructions for landing areas, antimechanized obstacles, and barriers for close-in all-around defense are of extremely limited value unless they are covered by fire.
75. OBSTRUCTION OF LANDING AREAS.-a. Obstacles to prevent the landing of aircraft are called obstructions. Plans may call for obstructing all landing areas in the vicinity of the airdrome, including those on which gliders or planes might be successfully crash landed. Reconnaissance of adjacent areas not used by friendly air forces must be undertaken to determine the obstruction necessary and the feasibility of placing it. Such locations should be blocked with permanent rather than temporary obstructions. They are spaced so that a landing plane will strike at least two in a run of 100 yards. Since airborne troops will be used to clear landing areas, the obstructions must be difficult to remove.
b. The best obstruction is a ditch or trench. A series of shallow trenches about 3 feet wide and 6 feet long dug at 50-foot intervals is effective. If time permits, the spoil should be removed so that it will not be available for filling. A variation is a series of hummocks of earth irregularly spotted at 50-foot intervals and made by excavating at a distance of 10 to 12 feet around a point and throwing the spoil to the center. Another method of obstruction consists of checker-boards of double furrows spaced to form 100-yard squares. Rows of posts are effective but require considerable time to place. Various other obstructions afford a measure of security. Large and heavy objects such as concrete pipes, concrete blocks, useless vehicles, rock-filled drums, steel tetrahedrons, or cut trees will suffice. Roads which might be used for the landing of air transports can be blocked by putting obstacles along the shoulders high enough to catch the wings or by stretching cables across the road high enough to permit the passage of vehicles.
c. The successful temporary obstruction of operational fields and runways is difficult. About the only quickly placed temporary obstructions are motor vehicles which can be driven on and parked or objects which can be hastily towed into position. The unused portion of landing grounds in operation should not be permanently blocked. as night landings of friendly planes, without lights and under various weather conditions, are in themselves sufficiently hazardous without further complications.
76. ANTIMECHANIZED OBSTACLES.-Concealed or camouflaged obstacles should be used on all approaches to the airdrome which are not needed for its defense. Even though a ground mechanized threat does not exist, protection should be provided against tanks light enough to be transported by air. (See FM 5-30 concerning location and construction.)
77. BARRIERS AGAINST PERSONNEL.-At airdromes where the situation indicates possibility of attack by airborne or ground troops, all positions which are to be defended should be given as complete wire protection as will not interfere with concealment. The order of erecting available wire should be around gun emplacements near the outskirts of the defense, around gun emplacements within the defended area, around other defense positions, and across access to more dangerous avenues of approach and defiladed areas. Defense wiring should be carefully planned to prevent disclosure of positions. Symmetrical or circular outlines are normally avoided. The construction of common types of protective wiring is shown in FM 5-15.
SECTION V: ALARM SYSTEMS
78. LOCAL ALARM SYSTEM.-An effective local alarm system is essential. Normally every airdrome will be included in an Aircraft Warning Service (see FM 1-25) established by higher authority which will notify the local airdrome commander of the approach of hostile aircraft. Warning will also be received from the Antiaircraft Artillery Intelligence Service (see FM 4-106). A local alarm system of sentinels and observation posts, adequate communications, and warning signals, is, however, necessary to supplement outside warning services and to alert personnel upon hostile approach.
79. SENTINELS AND OBSERVATION POSTS.-Sentinels should be posted and observation posts maintained at strategic points outside the airdrome to give the alarm for approaching hostile aircraft, to warn of chemical attack, and to act as spotters in case of airborne or ground attack. Personnel at these posts should be trained in the recognition of air-craft. All areas likely to be attacked by airborne or ground troops must be kept under continuous observation. Spotters must be on the alert for parachute or air-landing troops and be prepared to guide friendly troops to their landing places. Provision must be made for the immediate verification of reports of the dropping of parachute troops. In friendly territory maximum advantage should be taken of the services of civil organizations which can be formed and trained to report attacks by parachute troops, air-landing troops, or mechanized forces. An AAAIS, if present, will provide the basis for an observation system.
80. COMMUNICATIONS.-The observation system is comparatively useless without unfailing communications. Telephone, radio, and improvised signals must be ready for immediate report of impending attack. The time for warning is often so short that vehicles or runners will not suffice. Complete dependence cannot be placed on any one method of communication (see par. 44b). The signal system must also provide for the rapid communication of warning to higher headquarters or to the nearest agency of the Aircraft Warning Service.
81. WARNING SIGNALS.-A set of signals, both audible and visual, must be devised for warning personnel. The system should be based on a general alarm signal, preferably a siren or special horn, to alert the command. This signal can be followed by another general signal which will send all personnel to battle stations. Special signals are needed. If the hostile mission is one of aerial bombardment only, as much of personnel as possible will take cover, but to resist airborne attack or ground attack local ground defense plans must be put into operation. Special signals, such as the striking of a steel triangle or the sounding of a klaxon horn or combinations of signals, must be available for gas attack. Means to give information or orders may be required. Local signal codes are extremely useful and not difficult to improvise. A loud speaker system has many advantages.
SECTION VI: DAMAGE CONTROL
82. GENERAL.-Provision must be made for emergency damage control. Fires must be controlled and incendiaries dealt with immediately. Communications must be maintained. Decontamination of installations essential to the defense may be necessary. Damage to vital installations must be given emergency repair if it is required that the airdrome continue to operate under attack. If friendly planes are in the air or are to be put into the air, one runway must be kept in condition for use. Speedy repairs depend largely on advance preparations and training and the use of equipment rather than hand labor. (See TM 5-255.)
83. PLANS AND COORDINATION.-Detailed plans and effective coordination are required. A damage control officer should be appointed to assist the defense officer by directing all repair activities. Details must be organized to control and repair damage as it occurs. Fire plans and efficient fire-fighting squads must be ready. Details must also be organized for the maintenance of communications and the repair of runways. Damage control details will normally be organized from appropriate service troops available, augmented if necessary by specially trained Army Air Forces personnel. During an attack only the minimum repair details will be exempted from the general defense and will be at emergency stations. Additional personnel, if required, will be obtained from the fighting personnel under control of the defense officer.
84. REPAIRS AFTER ATTACK.-All service personnel who can be spared will be released by unit commanders to work under the general supervision of the damage control officer. To survey the extent of damage and to establish priority of work, a hasty reconnaissance should be undertaken immediately.
SECTION VII: PROTECTION AGAINST CHEMICALS
85. GENERAL.-All personnel must be trained and conditioned so that they will be able to carry out their duties promptly and efficiently during a chemical attack. Chemical defense plans must be based on what the enemy can do, not on what it is thought he will do.
■86. GAS DISCIPLINE.-Gas discipline is essential. All personnel should feel that the security of the command depends upon the orderly and prompt execution of the protective procedures in which they have been drilled.
87. PROTECTION BY DISPERSION.-Dispersion of aircraft and airdrome facilities, installations, and equipment is a primary means of defense against chemical attack.
88. PROTECTION BY GASPROOFING.-Materiel and installations necessary to the functioning of the airdrome must be protected against chemicals. The communications center and the operations and control centers should be gasproof. Although it is neither necessary nor feasible to provide gas-proof protection for all installations at an airdrome, every structure which is protected against bombing can be gas-proofed. Those structures which are to be protected against gas must also be at least blastproof and splinterproof. (See FM 21-40 and TM 5-310.)
89. RUNWAYS AND LANDING AREAS.-Chemical agents do relatively little direct damage to runways or landing areas, although mustard type agents will contaminate the grass on turfed fields. The greatest difficulty will result from the use of persistent gas to delay repair of damage caused by high explosives. The contamination of a large area of a runway or landing ground will, however, interfere with its use by air-craft. Neutralization of the chemicals by prompt decontamination is the primary defensive measure. For bomb craters or for small areas satisfactory results can be had from the standard demustardizing apparatus, but for larger areas, such as runways, a motor-driven unit is required. No special measures against incendiaries are necessary other than to keep grass and brush cut back from dispersed aircraft and buildings.
90. PROTECTION OF AIRCRAFT.-If possible, aircraft should be protected from contact with liquid chemicals, but revetments which are proof against chemicals in liquid form will not ordinarily be provided. Overhead cover for large bombardment planes is not normally practicable. Except for the largest planes, however, protection against overhead and drifting sprays should be provided. Covers of impermeable material for cockpit, engine, and propellers are effective and should be employed, when available, to protect planes not being used or serviced.
91. EXPLOSIVES AND INFLAMMABLE STORES.-Explosives and inflammables are not appreciably affected by chemicals except when the liquid comes in contact with metallic containers. Storage of gasoline and other fuels underground adequately protects them from chemical contamination as well as from incendiaries under ordinary conditions. Magazines and similar buildings used for storing explosives give sufficient protection. Bombs, munitions, gasoline, oil, and equipment stored in the open should be protected by gas-proof tarpaulins.
92. FACILITIES FOR REPAIR AND MAINTENANCE.-The protection of facilities for repair and maintenance will vary with the degree of exposure of the airdrome and the time, personnel, and materials which are available for construction. If bombproof repair shops are built, they should also be gasproofed. Easily damaged equipment, such as parachutes and bomb sights, should be kept in blastproof, fire-resistant gasproof storage.
93. PROTECTION OF PERSONNEL.-a. General.-Personnel should be required to have gas masks available at all times and, since attack by persistent chemicals is one of the best means for neutralizing an airdrome, should be provided with clothing impregnated for protection. Each man should have a designated place to go during chemical attack, and should be drilled to go immediately to his place without confusion. With only those exceptions necessitated by the defense plan, these places should provide overhead and vertical protection against chemical spray.
b. Gas alarm system.-The "alert" signal announcing the probable approach of hostile planes should be the signal for waking sleeping personnel, closing gasproof shelters, and covering airplanes, trucks, food supplies, and water. The "gas alarm," however, should not be given until it is necessary for men to mask. Alarms should be located over the airdrome to relay the warning from any one part of the field to all others. The main alarm should be located at the operations office, and auxiliary alarms should be placed where men are habitually at work.
FIGURE 18.-Camouflaged auxiliary alarm made from truck axle.
c. Gas sentries.-Gas sentries should be posted at or near all gas alarms, gasproof shelters, working parties, and sleeping men. Guards stationed at the headquarters of various units and at important installations should also be trained in the duties of gas sentries.
d. Shelters.-Gasproof shelter can normally be provided only for those installations that must be kept in operation during the attack. Installations seriously impaired in operating efficiency when personnel is masked should be given priority. One or two bombproof gasproof shelters may be placed at each end of the landing area, one at the operations office, and one at the first aid station or at any other important installation. Personnel engaged in activities requiring a number of men should at a minimum be provided with overhead cover adequate to protect them from spray and with vertical cover, such as that afforded by impermeable paulins, which can be shifted as the wind changes. Impervious covers should be liberally provided for fox holes.
e. First aid.-The medical service should provide a special organization for the prophylaxis and treatment of gas cases.
f. Warning signs.-Warning signs should be promptly posted at all contaminated areas. Vigilance is required to prevent contamination from contact with objects, structures, and ground splashed with vesicants. The first to move after the attack must be the decontamination squads, which must prepare and mark off paths before activities can be resumed safely.
g. Decontamination stations.-Men contaminated by liquid chemicals must be required to report at once to a decontamination station. Assembly points can be designated in distant areas so that contaminated men may be transported by truck.
94. PROTECTION OF DEFENSE INSTALLATIONS.-Few defense installations can be protected against chemicals. Antiaircraft guns cannot be given protective cover and still function. At such installations protective clothing must be worn. Other weapons may be given cover overhead against spray, but some men at each gun should wear masks and protective clothing at all times when attack is possible. Frequent changes of shifts are necessary to reduce fatigue caused by wearing such clothing.
95. CHEMICAL WARFARE DEFENSE CENTER.-Separate storage should be given to materials and equipment used for decontamination. Decontamination squads should assemble at the storage point upon the "alert" signal.
96. PLANS.-For every airdrome an integrated chemical defense plan is required. Because of the technicality of the defense measures and the specialized training necessary, Chemical Warfare Service troops should be available for its execution.
97. REFERENCES.-See FM 21-40 and TM 5-310.
SECTION VIII DEMOLITION
98. GENERAL.-a. If an airdrome is liable to capture and if its possession intact would be of material advantage to the enemy, plans for its defense must include measures to prevent or delay its use by him. The complete demolition of an airdrome, however, is a major operation which requires time and a large amount of explosives. Although installations and equipment present no unusual problem, the destruction of landing areas is difficult. Lack of time may prevent complete demolition. The following list suggests priorities and personnel for demolition:
(1) Runways and taxiways-aviation engineers.
(2) Remainder of landing area-aviation engineers.
(3) Routes of communication to the airdrome-engineers.
(4) Construction equipment at the airdrome-aviation engineers.
(5) Technical buildings-air force ground troops with engineer help.
(6) Supplies of gasoline, oil, and bombs-air force ground troops.
(7) Motor vehicles and unserviceable aircraft-air force ground troops.
(8) Housing-air force ground troops with engineer help.
b. Accomplishment of the complete list of demolitions would so effectively destroy the airdrome as to deny its use to the enemy without an entire rebuilding.
99. METHODS.-The methods of carrying out demolition must be decided on the location, as they will largely depend on the time available and the type of constructions. Paved runways present the most difficult problem. They may be cratered by means of explosives or torn up by mechanical grubbers. Bangalore torpedoes may be placed when the occasion arises in holes under the runways made by horizontal drills, or in culverts constructed at a depth of about 30 inches when the runway was built. To crater a runway effectively will require rows of charges placed across the run-way at 5-yard intervals every 100 yards, a task requiring much time, trained personnel, and a large amount of explosive. Grassed landing areas can be destroyed with moderate effectiveness by bulldozing or plowing 20-foot bands across them every 50 yards. Wet weather operation may be impeded or prevented if patches of the turf are killed by spraying heavily with engine oil. Booby traps planted in damaged areas, underneath soil and tied to obstructions, will slow reconstruction. The standard demolition procedures described in FM 5-25 may be applied to installations and facilities. If it appears that a well-camouflaged field will fall into enemy hands without complete or effective demolition, it should be marked for subsequent bombing by some readily discernible sign which will be difficult to remove. Such a mark may be made by plowing, burning, or staining the runways portion with a cross approximately 100 yards across.
